我如何在运行时在 clojure 中定义 java class 并实例化它

Question

我尝试使用 clojure.core 中的 gen-and-load-class，然后使用自定义 class 加载程序来调用 defineClass 生成的字节码，但是当我调用

(foo.bar.MyClass.)

我得到

CompilerExceptionjava.lang.NoClassDefFoundError: Could not initialize class foo.bar.MyClass

更新：

所以我按照@Elogent 的建议使用了 deftype :

(defprotocol Struct
  (getX [this path] "Get value")
  (setX [this ^long value path] "Get value"))
(deftype Foo 
  [
  ^{:tag long :unsynchronized-mutable true} a 
  ^{:tag long :unsynchronized-mutable true} b 
  ^{:tag long :unsynchronized-mutable true} c]
  Struct
  (getX
    [this [head & tail]]
    (let [field (condp = head
          'a a
          'b b
          'c c)]
      (if (empty? tail)
        field
        (getX field tail))))
  (setX
    [this value [head & tail]]

    (if (empty? tail)
        (condp = head
          (set! a (long value))
          (set! b (long value))
          (set! c (long value)))
        (condp = head
          (setX a value tail)
          (setX b value tail)
          (setX c value tail)))))

在 AOT 之后当我做 javap Foo.class 我得到：

public final class struct.core.Foo implements struct.core.Struct,clojure.lang.IType {
  public static final clojure.lang.Var const__0;
  public static final java.lang.Object const__1;
  public static final clojure.lang.Var const__2;
  public static final java.lang.Object const__3;
  public static final clojure.lang.Var const__4;
  public static final clojure.lang.AFn const__5;
  public static final clojure.lang.AFn const__6;
  public static final clojure.lang.AFn const__7;
  public static final clojure.lang.Var const__8;
  public static final clojure.lang.Var const__9;
  public static final clojure.lang.Var const__10;
  public static final clojure.lang.Var const__11;
  public static final clojure.lang.Var const__12;
  long a;
  long b;
  long c;
  public static {};
  public struct.core.Foo(long, long, long);
  public static clojure.lang.IPersistentVector getBasis();
  public java.lang.Object setX(java.lang.Object, java.lang.Object);
  public java.lang.Object getX(java.lang.Object);
}

这正是我需要的。谢谢@Elogent！

Answer 1

除非你绝对需要 Java class 的所有灵活性，否则我建议你使用 deftype instead. As explained here，deftype 可以让你访问较低级别的结构例如原始类型和惯用方式的可变性。

我如何在运行时在 clojure 中定义 java class 并实例化它

How can I define in clojure a java class during runtime and instantiate it

clojure

gen-class